1. Field of the Invention
The present invention relates to a circuit for establishing a connection between a semiconductor IC device having a bidirectional I/O (input-output) terminal for receiving, for example, an active demand signal and transmitting an active demand acknowledge signal, which is a response to that received signal, and a semiconductor IC device having input and output terminals for respectively receiving and transmitting the above-described signals.
2. Description of Related Art
There has been a known circuit for establishing a connection between a semiconductor IC device having a bidirectional I/O terminal and a semiconductor IC device having individual input and output terminals. For example, a circuit of the type described above has been disclosed in Japanese Patent Laid-Open No. 60-96026. As shown in FIG. 15, the above-described circuit comprises a buffer circuit 50 capable of bringing its output to high impedance in response to a control signal, the above-described circuit further comprising another buffer circuit 51. The output of the buffer circuit 50 and the input of the buffer circuit 51 are connected to an I/O terminal 54 of a semiconductor IC device 52. On the other hand, the input of the buffer circuit 50 is connected to an output terminal 55 of the semiconductor IC device 53, while the output of the buffer circuit 51 is connected to an input terminal 56. Thus, when a control signal is properly supplied to the circuit, a signal can be sent/transmitted between the above-described two devices 52 and 53.
Hitherto, the devices have been connected as described above, or in a case where the semiconductor IC devices 52 and 53 are the components of an information processing apparatus, the devices have not directly been connected to each other, but a process by using a software has been performed so that the similar effect to the structure in which the semiconductor IC devices are connected to each other can be obtained.
However, the circuit shown in FIG. 15 encounters a problem as follows:
(1) A signal for controlling the buffer circuit 50 must be processed in an external circuit so as to be supplied to the buffer circuit 50.
(2) The output signal from the device 53 is supplied to the I/O terminal 54 and is also undesirably directly supplied to the input terminal 56 of the device 53 via the buffer circuit 51.
(3) In the case where the logical level of the input or the output signal is used as information in the device 53 and as well as the pulse signal is used as information in the device 52, information cannot correctly be supplied/received in the circuit shown in FIG. 15 in which the terminals are simply connected to each other by a buffer circuit.
In a case where the process by using a software is performed as an alternative to the direct connection of the devices, a great quantity of system design calculations are necessary and the volume of the software for the system cannot be reduced.